High Voltage Direct Current (HVDC) is increasing in usage due to a number of benefits compared to AC (Alternating Current) for power transmission. In order to connect a HVDC link or an HVDC grid to an AC grid, conversion needs to occur from DC (Direct Current) to AC or AC to DC. This conversion can for example be performed using voltage source converters (VSC).
In order to reduce harmonic distortion in the output of converters multilevel converters have been introduced, where the output voltages can assume several discrete levels. In particular, converters have been presented where a number of converter cells, each containing a number of switching elements and an energy storage element, are connected in series to form a variable voltage source.
There is always a drive to reduce losses of such converters, while still providing appropriate capabilities for switching control and fault handling.